Spectrum sharing is one of the most viable ways of improving the amount of spectrum available to wireless networks and other radio devices for conducting wireless communications. An exemplary spectrum sharing technique involves use of television white spaces under regulations set forth by an appropriate regulatory agency. An exemplary regulatory agency that regulates the use of wireless spectrum is the U.S. Federal Communications Commission (FCC). Other countries may have similar regulatory entities.
In the U.S., for example, the FCC has eliminated analog television (TV) broadcasts in favor of digital TV broadcasts. This has freed spectrum channels for use by unlicensed radio systems to offer various services, such as mobile communications and Internet access. In this context, the freed spectrum is commonly referred to as TV white space (or TVWS) but other types of white spaces are possible. In the case of TV white space, the white space includes unused spectrum that is interleaved with spectrum used by incumbent radio devices in the channel 2 to channel 51 range (corresponding to 54 MHz to 698 MHz). Exemplary incumbent radio devices for TV white space include television broadcasters and other priority users of television channels.
Under FCC regulations, for example, radio devices that use TVWS must contact a central database server (also referred to as a spectrum management server) and receive a channel list (also referred to as a channel map) of available channels for which the radio device may use in a shared environment with other TV band devices (TVBDs). The channel list that is generated for a TVBD by the central database server is based on the location of the TVBD and its radio characteristics. In this manner, the operation of incumbent radio devices having protected areas in which the TVBD is located will be taken into account when determining channel availability.
A concern expressed by the operators of incumbent radio devices is how the incumbent spectrum use will be protected from the potential effects of interference by TVBDs. The solution of choice is a geo-location database (e.g., the above-noted central database server) that is capable of managing the allocation of spectrum in accordance with policies defined in terms of geography, time, frequency and other application parameters, such as transmit power and emissions characteristics. But this methodology is predicated on a radio device being able to accurately report its location and characteristics (such as antenna height, gain, and emissions characteristics). If a device reports a location that is not accurate, the device may gain access to spectrum for which it would not otherwise have been permitted to use. Therefore, inaccurate location reporting may result in a higher likelihood of interference.
The process of spectrum management by a geo-location database system to protect the operation of incumbent radio systems relies on geographic coordinates reported by managed radio devices to be relatively accurate. For example, a geo-location database that operates in accordance with white spaces regulations, such as those promulgated by the FCC in the U.S. under 47 C.F.R. §15.701 et. seq., uses the location reported by a TVBD in a channel allocation request to provide a channel list of available TV white space channels to the TVBD for use in wireless communications by the TVBD. To provide an accurate list of available channels, the reported location is required by the FCC rules to be accurate to ±50 meters.
The accuracy requirement is used to ensure that the geographic coordinates are precise enough to provide effective protection for incumbent spectrum users. Additionally, separation distances between the white spaces radio and the protected radio devices are defined by contours that are specified such that the distances are adequate to provide protection based on the degree of location accuracy (e.g., the above-noted ±50 meters to TVWS). But the FCC regulations for TV white spaces only specify a single accuracy requirement and, correspondingly, only specify one set of separation distances. So if the radio cannot determine its geographic coordinates to the required accuracy, the radio is not permitted to receive a spectrum allocation.
For portable devices, such as mobile telephones, tablet computers, etc., the current location of the device is typically provided by a built-in geo-location determination technology of the device, such as GPS. Fixed location devices also may use this approach. But an incorporated geo-location capability cannot always provide sufficient accuracy. For example, a device located indoors or in a highly obstructed environment may not be able to determine its location using GPS within an accuracy of ±50 meters.
An example of a geo-location determination technique that has relatively low precision (e.g., location accuracy of greater than 50 meters) is GPS with an indicator of precision (e.g., a dilution of precision or DOP) that indicates a relatively low accuracy in the determined location coordinates. Another example is Apple Inc.'s “iOS horizontalAccuracy” (unspecified confidence). Google Inc.'s “Android location.GetAccuracy” (68% confidence) also has location accuracy of greater than 50 meters. Other examples include cellular site triangulation and WiFi access point proximity (e.g., as a service available from Skyhook Wireless, Inc. of Boston, Mass.).